Alternative control methods

Sanitation

Avoid introducing any new plant material that may contain leafminer eggs or larvae into the greenhouses. Rogue out severely infested plants. Promptly remove or destroy all crop residue containing larval leafminers that could continue to develop after harvest. Use physical barriers, such as hanging sheets of plastic, to prevent adults from flying to other areas of the greenhouse during harvest.

Host plant cultivar

Leafminers prefer and develop better on certain crop cultivars.A plant's chemical content, nutritional value, and the distribution and density of its hairs influence the plant's attractiveness to leafminers. Eliminate the most susceptible cultivars, if possible, or isolate them to reduce contamination to other cultivars. Chrysanthemum cultivars vary widely in their susceptibility to foliar damage by leafminers. In general, standard chrysanthemum cultivars suffer less damage than spray types. In one experiment, White Iceberg and Yellow Iceberg had significantly more mines than 15 other cultivars, while Statesman had the fewest mines. In other experiments, foliage of the cultivars Albatross, Bright Yellow Tuneful, Colonel Comfort, Divinity, Nob Hill, Pink Marble,and Sea Foam had less damage than did Iceberg.

Insect screens

Leafminers may invade greenhouses during the summer. Screens on vents, side-walls and doors will help prevent leafminers from migrating into the greenhouse from outside. However, proper screen installation is necessary in order to avoid reducing air flow.The maximum hole size to exclude L. trifolii is 640 p.

Greenhouse floor

The material beneath benches affects adult leafminer emergence. Fewer leafminer pupae survive in gravel under the benches than in soil. Leafminers that tried to pupate on polyethylene sheeting under tomato plants drowned when the greenhouse was watered. Ants killed many of the prepupae when the plastic was dry. However, pupal parasites of leafminers, such as Dacnusa sibirica or Opius spp., were also killed.

Fertilization

Nutrient inputs can affect pests as well as the plant. High levels of nitrogen are associated with leafminer problems, as well as spider mite infestations, on chrysanthemum. Avoid over-fertilizing crops.

Traps

Yellow sticky traps can be used for mass-trapping adult leafminers, as well as monitoring them.The traps do not catch many parasites of leafminers. Trapping adults reduced L. trifolii damage on chrysanthemum by 50% in experiments in Canada.

Chemical control

Localized infestations, or high populations that need to be reduced before predator or parasite introduction, should be spot-sprayed with selective chemicals.

Horticultural oils, both refined petroleum distillate products and those made from vegetable oils, can kill leafminers and other insects.These horticultural oils may be toxic to some plants.Various brands are registered for use on vegetables and ornamentals in greenhouses to control many pests, including leafminers.

Azadirachtin is the active ingredient in commercial formulations of extracts from seeds of the neem tree. This natural compound is an insect growth regulator that has a very low mammalian toxicity. It is also effective as a repellent or anti-ovipositional treatment. Foliar applications kill leafminer larvae in the mines, and reduce leafminer pupation and adult emergence. Solutions of azadirachtin also have controlled leafminers on chrysanthemum for 4 weeks after soaking rooted cuttings for 2-4 hours. It is registered for use on greenhouse ornamentals and vegetable crops.

Abamectin is an insecticide derived from the naturally occurring soil microorganism Streptomyces avermitilis.It is not a selective chemical, so it should be used only as a rescue treatment if biological control fails. It is registered for control of leafminers and spider mites on ornamental plants in greenhouses.

Spinosad is an insecticide derived from natural metabolites produced under fermentation conditions by the actino-mycete Saccharopolyspora spinosa. It is especially efficacious against leafminers, caterpillars, and thrips, but has low to moderate impact on beneficials. It is registered for control of many pests on landscape ornamentals; check with your chemical supplier on availability for use on greenhouse ornamentals.

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